In recent years, in air conditioners disposed with devices such as a compressor and a blowing fan, a 3-phase brushless DC motor, for example, has been used as a power source of these devices.
Generally, a 3-phase brushless DC motor includes a rotor comprising a permanent magnet having plural magnetic poles and a stator having 3-phase drive coils. A current corresponding to the position of the rotor with respect to the stator is allowed to flow in the drive coils of this kind of brushless DC motor by a motor drive control device for controlling the driving of this motor. Thus, in the drive coils, a magnetic field corresponding to this current arises, and the rotor rotates.
Here, among methods of detecting the position of the rotor with respect to the stator, there is often used a method that uses three position detecting sensors disposed so as to correspond to each of the 3-phase drive coils. Examples of the position detecting sensors include Hall elements and Hall ICs. However, costs become higher when there are many of these position detecting sensors, and the size of the substrate on which the position detecting sensors are disposed ends up becoming large.
Thus, in Japanese Patent No. 3,483,740, there is disclosed a device where the number of Hall ICs that are to be used, which is ordinarily three, is made into two and these two Hall ICs are disposed such that the phases of position detection signals that the two Hall ICs detect are shifted from each other by π/2, whereby the device stably drives a motor.